Researchon Boardband Circularly Polarized Antenna

This paper is divided into three parts and the three antennas has been designed,which are broadband circularly polarized cross dipole antenna,Polarization Reconfigurable broadband circularly polarized cross dipole antenna and low sidelobe phased array antenna.First,this paper introduced a wideband circularly polarized cross-dipole antennafabricated on a double-layered printed circuit board(PCB)substrate for 2.45-GHz ISM band wireless communications.Unlike conventional cross-dipole antennas,the proposed cross dipole is designed with wide openends such that both impedance and axial-ratio(AR)bandwidthsare enhanced.In addition,to excite the CP radiation effectively,a curved-delay line providing an orthogonal phase differenceamong the cross-dipole elements is attached at the corners of thesequentially rotated elements.By choosing a proper radius of thecurved-delay line,a wide input impedance of the antenna canbe realized.The antenna is center-fed by a 50-coaxial cableand is placed above a square reflector to obtain a directional CPradiation pattern.With the advantage of centered feed,symmetric CP radiation patterns can be achieved across the entire operatingbandwidth.In order to broaden the circularly polarized bandwidth,the slot and the angle of the dipole are cut.This antenna has good circular polarization characteristics.An impedance bandwidth(for VSWR<2)of about 41.5%(2.08~3.17 GHz)andthe 3-d B AR bandwidth of about 32.8%(2.19~3.05 GHz)around thecenter frequency of 2.45 GHz were simulated.The antenna has the maximum gain of 7.05 d Bacross the operating bandwidth.The size ofantenna is 0.45?*0.45?*0.23?.The second antenna is based on the first antenna,adding 12 PIN diodes,controlling the electric current,which achieve the effect ofthe controlling electromagnetic wave phase difference.The antenna can achieve the effect of reconstruction of left and right circular polarization.An impedance bandwidth of about 43%(2.08GHz~3.22GHz)when the antenna operates in the left-hand circular polarization state,and simulated results of the impedance bandwidthof about45%(2.06GHz~3.2GHz).The AR bandwidth of about 31.1%(2.28GHz~3.12GHz).An impedance bandwidth of about 44%(2.1GHz~3.3GHz)when the antenna operates in the right-hand circular polarization state,and simulated results of the impedance bandwidthof about47%(2.07GHz~3.35GHz).The AR bandwidth of about28.5%(2.35GHz~3.13GHz).The third is a low sidelobe phased-array antenna with the first antenna as an array element.The array uses 64 cells,arranged in a phased array of 8*8.Using the technology of unit autogyration,the axial ratio of the array antenna is optimized,and the negative influence of the antenna array to the AR is overcome.The AR of the antenna in the scanning angle is less than 3d B.The Taylor distribution is used to realize the characteristic of low side lobe.